There are numerous structures known for monitoring the level of liquid in a vessel, such as a tank, vat or sump, and either providing outputs indicative of the level or taking various actions in response to the level, or both.
Many different level sensing technologies have been used or proposed for such structures. For example, some such systems are based on sensors responsive to changes of pressure, indicative of changes in liquid level. Other systems rely upon the use of electrical probes whose electrical properties change with changes in liquid level. However, many popular systems rely upon sensing the vertical displacement of a float floating on top of the liquid.
Float mechanisms have been used in a variety of ways.
In a conventional arrangement, a single float rises to a certain pre-determined level, at which point an electrical switch or contact of some type is closed, thus energizing an associated electrical circuit, such as an alarm or a pump motor.
Various systems disclose the use of multiple floats to perform multiple functions. For example, U.S. Pat. No. 3,932,853 discloses the use of one float to operate a sump pump in the normal manner and the use of a separate float to operate an independent mercury switch to trigger an alarm circuit. Similarly, U.S. Pat. Nos. 4,187,503, 4,255,747 and 4,456,432 disclose alarm devices operated by their own float mechanisms separate and apart from the normal operation of their respective sump pumps. A difficulty with such systems is that the use of multiple floats to control operation of multiple electric circuits can be problematic. For example, particularly as the number of electric circuits and floats increases, it may become difficult to locate same in the vessel or sump without interfering with each other.
One of the difficulties of a float-based system is the need to avoid cycling of the pump at or around a desired liquid level. For example, if a float actuator is arranged to trigger operation of a pump motor (and pump) at a particular level as soon as the pump has reduced the liquid level just below the target level, then the pump will turn off. If liquid is continuing to enter the vessel, then the liquid level will rise again, thus triggering pump operation again, thus causing the liquid level to drop until pump shut off, etc.
To avoid such cycling, it is well known to provide a structure by which the pump will turn on at a specified upper level, but only turn off at a specified lower level. There are many such structures directed to such end. For example, in a pivoting float arrangement, it is known to have a float attached to a pivoting arm. Inside the float, a movable weight is either momentarily held in position as liquid level changes or must traverse a specified distance before engaging another component, in either case causing a lag between the time when the operation is triggered and then subsequently shut off. Examples of such mechanisms are disclosed in: U.S. Pat. No. 4,755,640 (disclosing a weight slidably mounted on a shaft, with the weight having step and groove structures to delay movement of a weight which engages and disengages a switch) and U.S. Pat. No. 5,728,987 (disclosing a structure in which a ball moves within a raceway to control the position of an operating rod which in turn engages and disengages a switch).
As a further example, it is also known to provide a float mounted to a float rod which in turn is slidably connected to a pump activation mechanism. As liquid level rises, the float and float rod move upwardly until a lower stop on the float rod triggers the pump activation mechanism. At that point, the mechanism is then secured or latched in an ON position by a latching arrangement. As the pump operates, the liquid level decreases and the float and float rod move downwardly, with the lower stop on the float rod descending away from the pump activation mechanism. Eventually, an upper stop on the float rod comes into contact with the pump activation mechanism. At that point, as the liquid level continues to drop, the weight of the float and float rod is transferred to the upper stop and, when sufficient weight has been transferred, the latching arrangement releases to an OFF position, thus disengaging the pump. Examples of such latching mechanisms are disclosed in: U.S. Pat. No. 6,461,114 (disclosing a pivoting lever latched by a spring tab) and U.S. Pat. No. 6,474,952 (disclosing a movable actuator body slidably mounted to both the float rod and a housing).
As another but somewhat similar example, it is known to provide a float slidably mounted on a float rod. As liquid level rises, the float moves upwardly on the float rod until the float engages an upper stop on the float rod. As liquid level rises further, the float then pushes the float rod upwardly until the pump mechanism is triggered. At that point, the float rod itself is then secured or latched in position. As the pump operates, the liquid level decreases and the float moves downwardly, away from the upper stop on the float rod, until eventually the float comes into contact with a lower stop also attached to the float rod. At that point, as the liquid level continues to drop, the weight of the float is transferred to the lower stop and, when sufficient weight has been transferred, the latching mechanism releases the float rod, thus disengaging the pump. An example of such a latching mechanism is disclosed in: U.S. Pat. No. 5,155,311 (disclosing a magnetic latching arrangement).
The possibility of using a single float in combination with multiple switches has been previously recognized. For example, U.S. Pat. Nos. 4,064,755, 4,186,419, 5,829,303 and 6,149,390 all disclose the use of floats which carry one or more magnets and interact with one or more fixed magnetic reed switches or magnetic microswitches. Such systems can suffer from a number of disadvantages. For example, the switches themselves are mounted inside a relatively large diameter tube where they are protected from the liquid itself. As a result, the floats are generally toroidal or dough-nut shaped with the tube passing through the central hole. Floats of such type can be more prone to jamming on the tubes thus possibly making such apparatuses potentially unreliable. In addition, magnetic reed switches or magnetic microswitches themselves can be expensive and limited in the amount of electric power they can handle, for example on the order of 100 W or less, and may not be adequate to directly handle the power required to operate many electric circuits that may have to be activated in response to rising liquid level in a vessel. For example, many such switches may not be suitable for direct use in a circuit with a 0.5 HP (about 370 W) AC sump pump motor drawing about 3 A at 120V, which in fact may draw significantly more power on start up. To energize such a system, conventional reed switches would likely have to be used in conjunction a suitable relay switch. However, such combination systems are both more complicated and more expensive and may be less reliable.
As another example, U.S. Pat. No. 4,086,457 discloses a pivoting float mechanism which contains two or more mercury switches oriented at different, predetermined angles to energize its associated electrical circuits. One difficulty with such a pivoting structure is that it may only effectively work over a relatively modest range of liquid levels. In addition, installation and calibration of the structure to operate at the desired liquid levels can be difficult and inconvenient and such difficulties can be compounded as attempts are made to add additional switches to the structure. Moreover, mercury switches can be expensive and there are environmental issues associated with their use and disposal.
In view of the above, there thus remains a need for a simple and reliable float switch apparatus for controlling the energization of multiple electric circuits in response to liquid level using a single float.